1. Field of the Invention
The present invention relates to easily forming an end-face window when semiconductor laser devices having emission wavelengths different from each other are manufactured on a substrate.
2. Description of the Related Art
Currently, an optical disk such as a DVD (Digital Versatile Disk) or a CD (Compact Disk) is actively used as a high-capacity optical medium which can record information in large quantities. A red semiconductor laser device of an emission wavelength of 650 nm is used in the DVD and an infrared semiconductor laser device of an emission wavelength of 780 nm is used in the CD.
Recently, in order to read both disks such as DVD and CD, an optical pick-up is used that corresponds to the both disks each including both a red semiconductor laser device having a wavelength of 650 nm and an infrared semiconductor laser device having a wavelength of 780 nm. The mainstream of conventional double wavelength semiconductor laser devices is a monolithic structure in which the red semiconductor laser device and infrared semiconductor laser device are located on a single substrate.
FIGS. 4A, 4B, 4C and 4D show a method of manufacturing a conventional double wavelength semiconductor laser device.
First, as shown in FIG. 4A, a double hetero structure 121 of an infrared semiconductor laser device 8 is formed on a first conductive-type (n) GaAs substrate 1. More specifically, the double hetero structure 121 of the infrared semiconductor laser device 8 is formed on the first conductive-type (n) GaAs substrate 1 by stacking thereon a first conductive-type (n) GaAs buffer layer 2, a first conductive-type (n) AlGalnP clad layer 3, an active layer 4 of multi-quantum well structure comprised of a GaAs well layer and an AlGaAs barrier layer, a second conductive-type (p) AlGalnP clad layer 5, a second conductive-type (p) GalnP intermediate layer 6, a second conductive-type (p) GaAs contact layer 7, and a second conductive-type (p) AlGaAs layer (not shown).
Next, after the second conductive-type AlGaAs layer is selectively removed in a stripe shape, the double hetero structure of the infrared semiconductor laser device 8 in an area where the double hetero structure of the red semiconductor laser device 15 is formed is removed by etching as shown in FIG. 4B.
Next, as shown in FIG. 4C, a double hetero structure 122 of a red semiconductor laser device 15 is formed on the first conductive-type GaAs substrate 1. More specifically, the double hetero structure 122 of the red semiconductor laser device 15 is formed on the first conductive-type GaAs substrate 1 by stacking thereon a first conductive-type (n) GaAs buffer layer 9, a first conductive-type (n) AlGalnP clad layer 10, an active layer 11 of multi-quantum well structure comprised of a Galnp well layer and an AlGalnp barrier layer, a second conductive-type (p) AlGalnP clad layer 12, a second conductive-type (p) GalnP intermediate layer 13, and a second conductive-type (p) GaAs contact layer 14.
Next, as shown in FIG. 4D, after the red semiconductor laser device 15 on the infrared semiconductor laser device 8 is removed, an end-face window structure is formed by masking apart excluding an end-face window portion is masked, depositing ZnO on the end-face window portion, and annealing the ZnO deposited portion at 600° C. to selectively diffuse Zn. At this time, in the end-face window structure, active layers of the double hetero structure of the red semiconductor laser device 8 and the double hetero structure of the infrared semiconductor laser device 15 include Zn of approximately 3e18 cm−3.
As a patent document describing the above mentioned simultaneous formation of the end-face window structure of the double wavelength semiconductor laser device, Japanese Unexamined Patent Application Publication No. 2001-345514 may be cited.
In the double hetero structure of a double wavelength semiconductor laser device, the end-face window structure serves, with ZnO as a diffusion source, penetrate Zn into an active layer via a second conductive-type clad layer made of AlGalnP in which phosphorus is a V-group mother element, thereby causing the active layer of a multi-quantum well structure to be disordered. The active layer 11 of the red semiconductor laser device 15 is disordered at a relatively low temperature of approximately 600° C. if the active layer includes Zn of 1e18 cm−3 or more. Meanwhile, the active layer 4 of the infrared semiconductor laser device 8 requires Zn of high concentration of 1e19 cm−3 or more at the same temperature as that of the active layer 11 of the red semiconductor laser device 15.
As described above, in the active layer 4 of the infrared semiconductor device 8, although Zn is required to be excessively diffused, when an end-face window structure is simultaneously formed, the diffusion of Zn to the active layer 4 of the infrared semiconductor layer 8 becomes insufficient. Hence, there arises a problem that sufficient disorder does not occur, and the active layer 4 does not serve as the end-face window structure.